This invention relates to spatial monitoring or surveillance and, more particularly, to an arrangement including an image sensor and a presence/movement detector.
In a monitoring arrangement disclosed in European Patent Document EP-A-0 772 168, which preferably is battery powered, a presence/movement detector serves to reduce current consumption by switching on an image sensor only when necessary. In a video monitoring system disclosed in United Kingdom Patent Document GB-A-2 309 133, an image sensor is connected to a video recorder. A presence/movement detector serves for more economical utilization of the magnetic tape on which images are stored, by switching on the video recorder only as needed. Such known surveillance arrangements store image information for evaluation by an attendant, which task is known to be monotonous and tedious. The arrangements lack intelligence, as events are not differentiated with respect to notification relevancy.
An arrangement disclosed in German Patent Document DE-U-297 18 213 includes an image sensor, a still-image generator and storage stage, a difference-image generator stage, and an image analyzer stage. An analytical result is compared with predetermined notification relevancy criteria, for a positive result to be reported to a central unit. As image sensor signals are automatically monitored for notification relevancy, this arrangement does have surveillance intelligence, with the central unit being notified of positive results only. However, as the image sensor depends on sufficiently intensive visible or near-infrared radiation, this arrangement may not be sufficiently robust in meeting security requirements.
In a spatial monitoring arrangement in accordance with the invention, intelligent monitoring has optimized discrimination and robustness. The arrangement includes at least one image sensor and at least one presence/movement detector connected to control and evaluation electronics including a processing stage for on-site, combined evaluation of sensor and detector signals.
This dual- or multi-criteria monitoring arrangement has significant advantages over known dual-notification devices, as well as over pure image sensors. The arrangement is significantly more robust than known dual-notification devices in which spatial resolution is coarse or absent, with the result that it is often impossible to differentiate between humans and animals. Furthermore, for intelligent monitoring the image sensor can provide for classifying objects based on their geometry and movement, and can provide for verification and storage of events for retrieval later.
As compared with pure image sensors, the arrangement in accordance with the invention is advantageous in that it can remain fully functional as a presence/movement detector even under poor lighting conditions. Furthermore, the detector can assist in interpreting difficult situations by automated processing.
In a preferred embodiment of an arrangement in accordance with the invention, signals from the image sensor and the presence/movement detector first are evaluated separately, before their combined evaluation.
A further preferred embodiment of an arrangement in accordance with the invention includes a CMOS (complementary metal-oxide-semiconductor) image sensor, preferably an active pixel sensor. Among advantages of CMOS image sensors over CCD (charge-coupled device) cameras are a power consumption which is lower by several orders of magnitude and the ability to access individual pixels. This latter feature enables readout of images with reduced resolution and of mere portions of interest of an image, whereas with CCD cameras the pixels can be read out only line by line.
In yet a further preferred embodiment of an arrangement in accordance with the invention, means is included for determining the distance of a detected object from the presence/movement detector, and passing the distance signal to aprocessing stage.